I'm aware, signing the package is not the same thing as signing the code. The application is built by the package maintainer(s) and then the resulting packages are signed.
Which is the same thing that Flatpak does. Both depend on the trust for the repo owner and the package maintainer.
Thanks for the tip! I took a look and it seems like Recognize uses this: https://github.com/jordipons/musicnn
Last update was 4 years ago but will give it a try this weekend.